“Tacks on ... or, when parsed as two words, what 17-, 28-, 47- and 63-Across all have?”

Sound at the beginning and end of a meditation, perhaps

Bit of smoke

Primate native to Madagascar

Where the Tigris and Euphrates Rivers meet

Up the ___ (raise the stakes)

Wipe off, as a blackboard

Gotham City SOS

Krypton and xenon

Casino machines